The present invention relates to a ceiling speaker system of an aircraft.
There are many small-sized speakers equipped to the passenger cabin of an aircraft for in-flight announcements.
It is important that all the passengers on board the aircraft are able to clearly hear the in-flight announcements, such as emergency guidance, which may be directly related to their safety. Therefore, in a conventional large-sized aircraft, three speakers are mounted on the lower face of the overhead compartment per one transversal row of eight passenger seats, the speakers spaced to correspond to the interval of the seats.
FIG. 11 is an explanatory view showing the cross-sectional structure of the conventional cabin of an aircraft.
The aircraft illustrated as a whole by reference number 1 comprises a body 10, a floor 30 disposed within the body 10, with rows of passenger seats 40 fixed to the floor 30. In the drawings, there are two passages (aisles) 32 separating the eight seats that constitute one transversal row of seats.
Overhead stowage bins etc. for stowing baggage are provided on the ceiling 20, and plural speakers 60 are mounted on appropriate positions of the bins etc. to provide in-flight announcements to the cabin 50.
There is approximately a 1.2-meter interval between one seat and the seat in front of or behind it.
A typical passenger cabin of an aircraft is as long as 40 meters, so there are approximately 100 speakers equipped within the cabin. The weight of one speaker is around 160 grams, so the total weight of speakers mounted on a mid-sized aircraft is around 16 kilograms. The wiring connecting the speakers is complex and also heavy.
Since the vibrating plate area of each of the small-sized speakers equipped in the aircraft is only approximately 44 cm2, the sound provided through the speaker is similar to that output from a point sound source having no surface area, which is diffused and attenuated in proportion to the square of distance. Therefore, even if the sound output through the speaker has a sufficient sound pressure level and may seem too loud near the speaker, the passengers seated somewhat far from the speaker cannot make out the sound clearly.
Reducing the number of speakers would only increase this undesired tendency, so many speakers must be equipped to the aircraft to assure comfort and safety of passengers.
Further, pleasant background music can be played through the speakers in the cabin to welcome passengers on board the aircraft, so it is preferable that the speakers output a high quality sound with a wide tone range. However, due to limited mounting space and weight, the miniaturization of the speakers is considered to be important and the quality of sound is thereby sacrificed.
The present invention aims at reducing the number of speakers on the aircraft so as to reduce the total weight and cost related thereto, without diminishing the comfort and safety of the passengers.
In other words, the present invention aims at providing a speaker system that minimizes the attenuation of sound from the speaker so that the sound is not too loud near the speaker but still reaches the whole cabin without fail.
The present invention solves the problem mentioned above by structuring the ceiling panels of the aircraft as a speaker having a large vibrating plate area, utilizing the characteristics that there is only small diffusion attenuation to the sound output from a surface sound source.
Since the sound from a surface sound source with a large surface area has directivity, only small diffusion attenuation occurs thereto.
Moreover, since the ceiling panels of the passenger cabin are aligned continuously along the axial direction of the aircraft, the sound output from the panels are free from attenuation in the axial direction when the ceiling panels are vibrated as a whole.
Even further, since the cabin has a cylindrical cross-section, diffusion in the direction orthogonal to the axis (the transverse direction) is suppressed, and theoretically the sound is delivered to every corner of the cabin of the aircraft maintaining appropriate volume.
There are a number of requirements listed later that the ceiling panels of the aircraft must fulfill in order to exert their fundamental functions. The ceiling panels according to the present invention are designed to fulfill all those requirements, and in addition, have appropriate sizes and flexural properties to function as acoustic vibrating plates realizing a ceiling speaker system.
An exciter is equipped to each panel so that all the panels are vibrated in phase by the power from an amplifier.